Aircraft have flight control surfaces on the leading and/or trailing edges of their aerofoil sections, such as the wings, horizontal tailplane, and vertical tailplane. Common leading or trailing edge devices are slats, flaps, spoilers, ailerons, elevators, rudders and air brakes. These flight control surfaces typically operate to provide enhanced lift or drag during low speed flight, for example take-off/climb and landing/descent, or to provide pitch, roll and yaw control during any of the flight phases.
Flight control surfaces are typically mounted to their aerofoil section by a supporting hinge fitting structure. Some flight control surfaces, particularly spoilers and ailerons, may be provided with slots in their leading edges in order to provide clearance to their supporting structure when the surfaces are moved. It is generally not practicable to cut back the supporting structure to provide a clearance, due to the weight penalty of structural reinforcement to counteract the stress concentration caused by the cut back.
It is highly desirable to seal these slots in order to reduce the aerodynamic parasitic drag (and therefore fuel consumption) and noise associated with the discontinuity in the surface. Furthermore, when some flight control surfaces, e.g. wing trailing edge flaps, are deployed, a void can be opened up in the lower aerodynamic surface of the aerofoil. The slot can act with the void to form an air path between the high-pressure zone on one side of the aerofoil and the low-pressure zone on the other side of the aerofoil. The migration of air from the higher-pressure zone to the low-pressure zone is known as “cross-bleed”, and can have a detrimental effect on lift performance. Since each flight control surface typically has at least two hinges, with as many a seven such surfaces on each aerofoil, the number of slots begins to have a significant effect.
Conventionally these slots are either left open and unsealed, or if the surface's kinematics and geometry allow, an attempt is made to fill the slot using deformable seals. A conventional method of sealing the slots is to provide elastomeric seals between the hinge fitting and the adjacent panels in order to fill the slots. However, the constant movement of the flight control surface over time often deforms or wears the seal to a degree that effective sealing is not possible. Constraints in the small size and need for adjustability often mean that it is impractical to fully seal the slot.
Spoilers are typically provided on the upper aerodynamic surface of the wing, between the main fixed wing portion and the trailing edge flaps. When the flaps are deployed, an effective gap is formed between the trailing edge of the spoiler and the leading edge of the flap. This gap can further enhance the lift performance of the flap. However, if this gap is too large and the continuity of the upper aerodynamic surface is not maintained, then the performance of the flap is reduced. To control the size of the gap, the spoilers are rotated downwardly or “drooped” when the flaps are deployed.
The practice of drooping spoilers poses particular problems for the sealing of the slots in the spoiler leading edge. The size of the effective slot may increase when the spoiler is drooped, exacerbating the problems described above if the slot is left un-sealed during flight phases where the preservation of high lift aerodynamic performance is particularly important. The angle of operation of a drooping spoiler will be large as the spoiler rotates in one direction when the spoiler is drooped and in the opposite direction when the spoiler is deflected upwards into the airflow. This angle of operation is often critical in determining the effectiveness and life of a slot seal. Repeated large movements could stretch the seal to the point where it is not able to return to its original shape and maintain effective sealing. Such large deflections may rule out the use of conventional elastomeric seals altogether.
Sealing of hinge slots at the edge of moveable aircraft panels is not limited to flight control surfaces and is an issue elsewhere on aircraft, e.g. landing gear bay doors. It is desirable to provide an effective sealing arrangement for all of these exposed slots.